 |
|
The NEI-VFQ-25 in People With Long-term Type 1 Diabetes Mellitus
The Wisconsin Epidemiologic Study of Diabetic Retinopathy
Arch Ophthalmol. 2001;119:733-740.
ABSTRACT
| |
Objectives To examine the association of the 25-item National Eye Institute Visual
Function Questionnaire (NEI-VFQ-25) overall and specific scale scores with
visual acuity, diabetic retinopathy, and other characteristics, in a cohort
of persons with type 1 diabetes.
Design Population-based cohort study.
Setting An 11-county area in southern Wisconsin.
Participants Six hundred two persons with diabetes whose conditions were diagnosed
when they were younger than 30 years and who were currently taking insulin
participated in baseline, 4-year, 10-year, and 14-year follow-up examinations.
Main Outcome Measures An interview that consisted of the 25-item NEI-VFQ was completed. Visual
acuity was measured by the Early Treatment of Diabetic Retinopathy Study (ETDRS)
protocol and the presence and severity of retinopathy and macular edema were
detected by masked grading of stereoscopic color fundus photographs using
the modified Airlie House classification and the ETDRS retinopathy severity
scheme.
Results Univariate analyses revealed that the total NEI-VFQ-25 score was lower
in persons who were older, had a longer duration of diabetes, higher glycosylated
hemoglobin, were in renal failure, had a history of cardiovascular disease,
hypertension, or amputation of a lower limb, had poorer visual acuity, more
severe diabetic retinopathy, macular edema, glaucoma, cataract, abnormalities
in tactile sensation or temperature sensitivity, smoked more total pack-years,
led a more sedentary lifestyle, and had poor peak expiratory flow. In multivariate
analyses, while controlling for the physical and mental component scores from
the Medical Outcomes Survey 36-Item Short-Form Health Survey as measures of
comorbidity, lower total NEI-VFQ-25 scores were independently associated with
poorer visual acuity, more severe retinopathy, older age, history of loss
of tactile sensation, and more total pack-years of cigarettes smoked.
Conclusions In this cross-sectional study, the 25-item NEI-VFQ seems to be strongly
associated with vision, independent of severity of retinopathy and other complications
associated with type 1 diabetes. It may be a useful measure of health-related
quality of life as it relates to vision in epidemiological studies and clinical
trials in persons with diabetes.
INTRODUCTION
THE NATIONAL Eye Institute Visual Function Questionnaire (NEI-VFQ) was
designed to measure vision-related functioning and the influence of vision
problems on health-related quality of life in persons with several eye conditions,
such as glaucoma, diabetic retinopathy, age-related cataract, age-related
macular degeneration, cytomegalovirus retinitis, and low vision.1
The questions constituting the instrument were developed from focus groups.
The reliability and validity of the instrument when used among people with
common eye conditions was tested and confirmed.2
However, to date there have been no population-based cohorts of people with
diabetes in which the associations of retinopathy and visual acuity with the
NEI-VFQ scales have been examined. The purpose of this report is to examine
the association of the NEI-VFQ-25 composite scores and specific scale scores
with visual acuity, diabetic retinopathy, and other characteristics, in the
cohort of persons with type 1 diabetes participating in the 14-year follow-up
of the Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR).
PATIENTS AND METHODS
STUDY POPULATION
The population, which has been described in previous reports,3-7
consisted of a sample selected from 10 135 diabetic patients who received
primary care in an 11-county area in southern Wisconsin from 1979 to 1980.
This sample was composed of "younger-onset" persons and "older-onset" persons.
These analyses were limited to the group of younger-onset persons, all of
whom were taking insulin and the conditions of all had been diagnosed when
they were younger than 30 years (n = 1210). There were 996 persons in this
group who participated in the baseline examination (1980-1982),3
891 in the 4-year follow-up,5 765 in the 10-year
follow-up,6 and 654 in the 14-year follow-up
(including 20 who had missed earlier follow-up examinations).7
The reasons for nonparticipation and comparisons between participants and
nonparticipants at baseline and the 4-, 10-, and 14-year follow-ups have been
presented elsewhere.3, 5-7
Mean ± SD and median lengths of time between the baseline and 14-year
follow-up examinations were 14.4 ± 0.5 years and 14.3 years, respectively.
PROCEDURES
The baseline and follow-up examinations were performed in a mobile examination
van in or near the cities where the participants resided. All examinations
followed a similar protocol that was approved by the institutional human subjects
committee of the University of Wisconsin–Madison. The pertinent parts
of the ocular and physical examinations included measuring refractive error
and best-corrected visual acuity for distance using a modified Early Treatment
Diabetic Retinopathy Study (ETDRS) protocol in which the charts were reduced
in size for a 2-m distance8-9;
measuring weight, height, blood pressure,10
and intraocular pressure; dilating the pupils; taking stereoscopic color fundus
photographs of 7 standard fields8-9;
performing a semiquantitative determination of glucose, ketone, and protein
levels in the urine using Labstix (Ames, Elkhart, Ind); and determining blood
glucose and glycosylated hemoglobin A1 levels from a capillary
(baseline) or venous (follow-up) blood sample.11-12
A structured interview was conducted by the examiners including questions
about specific medications for control of hyperglycemia and blood pressure,
the use of diuretic agents, the number of aspirin tablets taken during the
30 days before the baseline examination, and smoking. If there was any question
about medication use, it was verified by a physician's report. Other questions
included whether patients had experienced loss of sensation in their hands
or feet and decreased ability to feel the hotness or coldness of things they
touched since having diabetes.
After the interview, a measure of peak expiratory flow was obtained
for 3 trials. The measurement used in the analyses reflects the maximum peak
expiratory flow of the 3 trials.
From July 1997 to November 1998 (mean ± SD, 27 ± 6 months;
median, 28 months after the last eye examination), the NEI-VFQ-25 was administered
by telephone to 602 WESDR younger-onset subjects who had participated in the
1995-1996 examination.
DEFINITIONS
For each eye, the best-corrected visual acuity was recorded as the number
of letters read correctly from 0 ( 20/250) to 70 (20/10).13
For eyes with visual acuity worse than 20/250, 1 of 6 levels of visual acuity
was recorded: 20/320, 20/400, 20/800, hand motions, light perception, and
no light perception. This represents a continuation of the scale wherein a
loss of 15 letters is equivalent to a doubling of the visual angle or a significant
reduction in vision. These levels were assigned values on the visual acuity
scale of -5, -10, -25, -40, -55, and -70,
respectively. In this study, visual acuity was defined as the visual acuity
in the better eye, and blindness was defined as a visual acuity of 20/200
or worse in the better eye.
The grading protocol has been described in detail elsewhere and is a
modification of the ETDRS adaptation of the modified Airlie House classification
of diabetic retinopathy.6, 14-17
For each eye, the maximum grade in any of the 7 standard photographic fields
was determined for each of the lesions used in defining the "retinopathy levels."
The retinopathy level for a participant was derived by concatenating the levels
for the 2 eyes, giving the eye with the higher level greater weight. This
scheme provided a 15-step scale (10/10, 21/<21, 21/21, 31/<31, 31/31,
37/<37, 37/37, 43/<43, 43/43, 47/<47, 47/47, 53/<53, 53/53, 60+/<60+,
and 60+/60+) when all levels of proliferative retinopathy were grouped as
one level. For purposes of classification, if the retinopathy severity could
not be graded in an eye, it was considered to have a score equivalent to that
in the other eye. For purposes of tabulation, the number of severity levels
for individuals was reduced to 4: none if the retinopathy level was 10/10;
minimal nonproliferative diabetic retinopathy (levels 21/<21 to 37/37);
moderate to severe nonproliferative diabetic retinopathy (levels 43/<43
to 53/53); and proliferative diabetic retinopathy (levels 60+/<60+ to 60+/60+).
Panretinal photocoagulation was documented by the grading of fundus photographs.
Macular edema was defined as thickening of the retina with or without
partial loss of transparency within 1 disc diameter from the center of the
macula6 or the presence of focal photocoagulation
scars in the macular area associated with a history of development of macular
edema as documented by stereoscopic fundus photographs. Clinically significant
macular edema was based on the detailed gradings and was defined as the presence
of any 1 of the following: retinal thickening at or within 500 µm of
the center of the macula; and/or hard exudates at or within 500 µm of
the center of the macula if associated with thickening of the adjacent retina;
and/or a zone or zones of retinal thickening 1 disc area in size, at least
part of which was within 1 disc diameter of the center.18
Whenever we found new signs of photocoagulation scars in the macular area
in the absence of macular edema and we had not previously documented macular
edema by grading fundus photographs taken at an earlier examination, we obtained
fundus photographs from the participant's ophthalmologist. In the absence
of fundus photographs, we obtained medical records documenting that macular
edema due to diabetes had been present prior to the focal (or grid) photocoagulation.
For situations in which participants gave a history of laser photocoagulation
but there were no signs of treatment burns, we requested information from
the treating ophthalmologist to verify that such treatment had been done and
to ascertain whether macular edema had been present prior to focal laser treatment.
For purposes of analysis, macular edema was considered to be present in an
eye if graded as present in fundus photographs or if there was a documented
prior history of macular edema with focal photocoagulation treatment. If macular
edema could not be graded in an eye, the individual was assigned the score
of the other eye.
Age was defined as the age at the time of the 14-year follow-up examination
in 1995-1996. Age at diagnosis of diabetes was defined as the age at the time
the diagnosis was first recorded by a physician on the patient's medical record.
The duration of diabetes was that period between the age at diagnosis and
the age at the 14-year follow-up.
The means of both systolic and diastolic blood pressures were the averages
of the last 2 of 3 measurements according to the protocol of the Hypertension
Detection and Follow-up Program.8-9
Hypertension was defined as a mean systolic blood pressure greater than or
equal to 160 mm Hg and/or a mean diastolic blood pressure greater than or
equal to 95 mm Hg or a history of antihypertensive medication use at the time
of examination in individuals aged 25 years or older or a mean systolic blood
pressure greater than or equal to 140 mm Hg and/or a mean diastolic blood
pressure greater than or equal to 90 mm Hg and/or a history of antihypertensive
medication use at the time of examination in younger persons.
Cigarette smoking status was determined as follows: a person was classified
as having never smoked if he or she had smoked fewer than 100 cigarettes in
his or her lifetime, as being an ex-smoker if he or she smoked more than this
number of cigarettes in his or her lifetime but had stopped smoking before
the examination, or as currently smoking if he or she had not stopped. For
purposes of analysis, 2 dichotomous variables were defined: 1 to compare persons
who had formerly smoked with those who had never smoked and 1 to compare persons
who currently smoked with those who had never smoked. Pack-years smoked was
calculated as the number of cigarettes smoked per day divided by 20, multiplied
by the number of years of smoking. Proteinuria was defined as a urine protein
concentration of 0.30 g/L or greater as measured by Labstix. End-stage renal
disease was defined as having had a kidney transplant or receiving renal dialysis.
History of lower extremity amputation was ascertained by questionnaire or
direct observation. The 36-Item Short-Form Health Survey (SF-36) was administered
during the study.19-20 This was
reduced to the physical component summary and mental component summary.20 These summary measures reduced the 8 subscales of
the SF-36 to the physical and mental dimensions of health status. To adjust
for the independent effects of overall physical and mental health on the NEI-VFQ
scores, each multivariate model included the physical and the mental component
summary scores from the SF-36. In addition, all subjects were asked whether
their health was excellent, very good, good, fair, or poor (EVGFP scale).
In rating their physical activity, subjects were asked how many times per
week they engaged in a regular activity long enough to work up a sweat. A
sedentary lifestyle was defined as engaging in fewer than 3 such activities
per week.
STATISTICAL ANALYSES
The composite NEI-VFQ scale used in the analyses was a modified version
in which the general health question was the only item excluded. These analyses
gave results similar to those for the composite NEI-VFQ scale using the full
25 items. For univariate analyses of the 25-item composite scale, mean values
of the scale were calculated for categories of the independent variables.
Statistical significance of the associations was tested by the significance
of the Spearman correlation. Because the scale was skewed (Figure 1), a logarithmic transform was performed by the formula
TVFQ25 = ln (101-VFQ25), in which TVFQ25 and VFQ25 are the transformed and
untransformed values of the 25-item composite scale, respectively. The transformed
scale was used as the dependent variable in multiple linear regression.21 For ease of interpretation, the results are reported
in the original untransformed scale. Significant variables in the final multiple
linear regression model were examined for nonlinear effects by the addition
of quadratic terms. Interactions of age with other factors were also tested.
Univariate analyses of NEI-VFQ-25 subscales were performed similarly. Because
these scales are more discrete in nature and do not lend themselves to normalizing
transformations, multivariate analyses were performed by ordinal logistic
regression.22 The general vision, near vision,
far vision, and driving scales were divided into 3 groups, and the mental
health scale was divided into 4 groups.
|
|
|
|
Figure 1. Frequency distribution of the
National Eye Institute Visual Function Questionnaire-25.
|
|
|
RESULTS
The differences between responders and nonresponders (n = 52) are presented
in Table 1. Those who did not
respond were more likely to be older, have longer duration of diabetes, have
poorer visual acuity, and have more complications associated with diabetes.
|
|
|
|
Table 1. Selected Characteristics of Participants With and Without
VFQ-25 Scores in the WESDR, 1995-1996*
|
|
|
The distributions of the NEI-VFQ-25 and its subscales are presented
in Table 2. Few participants had
scale scores of 0, while a sizable proportion had scale scores of 100. Scores
for general health, general vision, near vision, far vision, and driving were
lowest, and those for peripheral vision, color vision, and visual pain were
highest.
|
|
|
|
Table 2. Distribution of VFQ-25 Composite and Subscale Scores*
|
|
|
Univariate analyses revealed that the total score was lower in persons
who were older, had a longer duration of diabetes, higher glycosylated hemoglobin,
were in renal failure, had a history of cardiovascular disease, hypertension,
or amputation of a lower limb, had poorer visual acuity, more severe diabetic
retinopathy, macular edema, glaucoma, cataract, abnormalities in tactile sensation
or temperature sensitivity, smoked more pack-years, led a more sedentary lifestyle,
and had poorer peak expiratory flow (Table
3 and Table 4). There
was no difference between men and women. Similar associations were found for
the general, near, and far vision subscales and the mental health score (data
not shown) and driving subscale scores. The associations with visual pain,
social functioning, role functioning, dependency, peripheral vision, and color
vision were not examined because deficits on these subscales were uncommon.
|
|
|
|
Table 3. VFQ-25 Composite and Select Subscale Scores by Various Characteristics*
|
|
|
|
|
|
|
Table 4. Correlations of Characteristics of the Population With VFQ-25
Composite Score and Subscale Scores*
|
|
|
While controlling for retinopathy severity level, age, pack-years smoked,
SF-36 physical component summary, SF-36 mental component summary, and the
loss of tactile sensation, the association of visual acuity with the composite
NEI-VFQ-25 score is shown in Figure 2.
Persons with visual acuity of 20/10 had a composite NEI-VFQ-25 score of 96.1
while those with visual acuity of 20/800 had a total score of 62.8. Because
of the transformation of the NEI-VFQ-25, the effect of the independent variables
was greater at higher values with the exception of visual acuity, the effect
of which was greater with poorer vision. However, visual acuity and the SF-36
physical component summary each had a significant quadratic term. For visual
acuity, the effect of this term was to decrease the effect of lower vision;
for the SF-36 physical component summary, the quadratic term increased the
effect at higher values. Visual acuity explained 27.1% of the variance (R2). Additional statistically significant associations
were found for retinopathy severity level (3.8%), age (0.8%), pack-years smoked
(1.6%), SF-36 physical component summary (12.8%), SF-36 mental component summary
(3.7%), and loss of tactile sensation (1.4%). These factors and visual acuity
explain 51% of the variance (Table 5).
|
|
|
|
Figure 2. Independent effect of visual acuity
on the total 25-item National Eye Institute Visual Function Questionnaire
score while controlling for age, retinopathy level, loss of tactile sensation,
pack-years smoked, SF-36 (36-Item Short-Form Health Survey) physical component
summary, and SF-36 mental component summary.
|
|
|
|
|
|
|
Table 5. Independent Effect of Each Variable on the VFQ-25 While Controlling
for Visual Acuity and All Other Variables*
|
|
|
Multivariate analyses of general, near, and far vision subscale scores
and the mental health and driving subscale scores again showed visual acuity
to be strongly associated with each of the subscale scores (data not shown).
While controlling for age, visual acuity, and use of glaucoma drops, persons
with panretinal photocoagulation in 1 or both eyes were more likely to report
a peripheral vision deficit than persons without panretinal photocoagulation
(odds ratio, 2.35; 95% confidence interval, 1.31-4.21).
COMMENT
The NEI-VFQ-25 has been shown to be a reliable and valid questionnaire
for patients with 5 chronic eye conditions or low vision from any cause.23 The data presented herein extend these findings in
a population-based cohort of persons with long-term type 1 diabetes in whom
visual acuity and diabetic retinopathy were measured using standardized protocols.
The NEI-VFQ-25 composite score and subscale scores associated most closely
with central vision (general, near, and far vision subscale scores and the
driving subscale score) are strongly and independently correlated with visual
acuity. These findings are consistent with those reported in 123 patients
with moderate to severe diabetic retinopathy who were participants in the
NEI-VFQ Field Test designed to assess the reliability and validity of the
51-item Field Test Version of the NEI-VFQ.2
In the WESDR, after controlling for visual acuity, there was a minimal
effect of more severe retinopathy on the NEI-VFQ-25 composite score (a reduction
from a total score of 93.7 in those without retinopathy to 88.8 in those with
proliferative retinopathy in both eyes). In our study, the effect of age-related
cataract on the NEI-VFQ-25 was also small once visual acuity was controlled.
These findings provide further evidence that the NEI-VFQ-25, independent of
the presence and severity of retinopathy or macular edema or cataract, is
a valid measure of vision-targeted health-related quality of life in epidemiological
studies and clinical trials of persons with diabetes.
Although this is the first report of the influence of diabetic eye disease
on multidimensional vision-targeted health-related quality of life as captured
by the NEI-VFQ-25, others have reported similar correlations between self-reported
measures of visual functioning and measured visual acuity among persons with
retinal disease in general,24 age-related macular
degeneration,25 glaucoma,26
and optic neuritis.27 Additionally, in this
cohort with diabetes, we have previously reported on the negative influence
of hyperglycemia and diabetic complications on general health-related quality
of life as measured by the SF-36.28-29
In a practice-based sample, Hanninen et al30
also found that patients with type 2 diabetes had poorer general health-related
quality of life than age- and sex-matched controls and that these decrements
were primarily attributable to diabetes-related complications, such as visual
impairment and coronary artery disease. A recent study that measured health
utilities to estimate the influence of visual loss attributable to diabetic
retinopathy identified substantial decrements in quality of life attributable
to diabetic eye disease.31
Care must be exercised when interpreting the results of this study.
First, the NEI-VFQ-25 was administered from July 1997 through November 1998,
a period of 1 to 3 years after completion of the study examinations. Changes
in visual acuity (both worsening and improvement) could weaken the association
reported. In addition, the lag period between the last eye examination and
the NEI-VFQ-25 interview might also explain some of the ceiling effect noted
on some of the subscales. This may have resulted because many of the nonresponders,
who had more severe disease, would be the ones most likely to have lower VFQ
scores. Second, the results are limited to persons with long-term ( 16
years) type 1 diabetes. Although the content of the NEI-VFQ-25 was driven
by information provided during focus groups with persons with chronic eye
diseases, it is possible that the participants with diabetes had decrements
in domains of vision-targeted health-related quality of life that are not
included in the NEI-VFQ-25.
In summary, strong associations are reported between best-corrected
visual acuity and the NEI-VFQ-25 composite and subscale scores associated
with central vision. Longitudinal data and information on people with type
2 diabetes are needed for further evaluation of the generalizability of these
findings.
AUTHOR INFORMATION
Accepted for publication September 25, 2000.
This research was supported by grants EYO3083 (Drs R. Klein and B. E.
K. Klein) and EY12198 (Drs R. Klein and B. E. K. Klein) from the National
Institutes of Health, Bethesda, Md; and in part by the Senior Scientific Investigator
Award from Research to Prevent Blindness Inc, New York, NY (Dr R. Klein).
We thank the 452 Wisconsin physicians and their staffs who participated
in and supported this study. We also thank the local hospitals that provided
supportive services for the mobile van, and the State of Wisconsin Division
of Health, Madison, for donating the van.
Corresponding author: Ronald Klein, MD, MPH, Department of Ophthalmology
and Visual Sciences, University of Wisconsin–Madison, 610 N Walnut St,
460 WARF, Madison, WI 53705-2397.
Ronald Klein, MD, MPH;
Scot E. Moss, MA;
Barbara E. K. Klein, MD;
Peter Gutierrez, MA;
Carol M. Mangione, MD
From the Department of Ophthalmology and Visual Sciences, University
of Wisconsin Medical School, Madison (Drs R. Klein and B. E. K. Klein and
Mr Moss); and the Department of Medicine, University of California School
of Medicine, Los Angeles (Mr Gutierrez and Dr Mangione).
REFERENCES
1. Mangione CM, Berry S, Spritzer K, et al. Identifying the content area for the 51-item National Eye Institute
Visual Function Questionnaire: results from focus groups with visually impaired
persons. Arch Ophthalmol. 1998;116:227-233.
FREE FULL TEXT
2. Mangione CM, Lee PP, Pitts J, Gutierrez P, Berry S, Hays RD for the NEI-VFQ Field Investigators. Psychometric properties of the National Eye Institute Visual Function
Questionnaire (NEI-VFQ). Arch Ophthalmol. 1998;116:1496-1504.
FREE FULL TEXT
3. Klein R, Klein BEK, Moss SE, Davis MD, DeMets DL. The Wisconsin Epidemiologic Study of Diabetic Retinopathy, II: prevalence
and risk of diabetic retinopathy when age at diagnosis is less than 30 years. Arch Ophthalmol. 1984;102:520-526.
FREE FULL TEXT
4. Klein R, Klein BEK, Moss SE, Davis MD, DeMets DL. The Wisconsin Epidemiologic Study of Diabetic Retinopathy, III: prevalence
and risk of diabetic retinopathy when age at diagnosis is 30 or more years. Arch Ophthalmol. 1984;102:527-532.
FREE FULL TEXT
5. Klein R, Klein BEK, Moss SE, Davis MD, DeMets DL. The Wisconsin Epidemiologic Study of Diabetic Retinopathy, IX: four-year
incidence and progression of diabetic retinopathy when age at diagnosis is
less than 30 years. Arch Ophthalmol. 1989;107:237-243.
FREE FULL TEXT
6. Klein R, Klein BEK, Moss SE, Cruickshanks KJ. The Wisconsin Epidemiologic Study of Diabetic Retinopathy, XIV: ten-year
incidence and progression of diabetic retinopathy. Arch Ophthalmol. 1994;112:1217-1228.
FREE FULL TEXT
7. Klein R, Klein BEK, Moss SE, Cruickshanks KJ. The Wisconsin Epidemiologic Study of Diabetic Retinopathy, XVII: fourteen-year
incidence and progression of diabetic retinopathy and associated risk factors
in type 1 diabetes. Ophthalmology. 1998;105:1801-1815.
FULL TEXT
|
ISI
| PUBMED
8. Procedures for completing eye examinations. In: Early Treatment Diabetic Retinopathy Study (ETDRS). Manual
of Operations. Baltimore, Md: National Technical Information Service;
1985:1-15.
9. Classification of diabetic retinopathy from stereo color fundus photographs. In: Early Treatment Diabetic Retinopathy Study (ETDRS). Manual of Operations. Baltimore, Md: National Technical Information
Service; 1985:1-49.
10. Hypertension Detection and Follow-up Program Cooperative Group. The Hypertensive Detection and Follow-up Program. Prev Med. 1976;5:207-215.
FULL TEXT
|
ISI
| PUBMED
11. Quick-Step, Fast Hemoglobin Test System. Akron, Ohio: Isolab; 1981:1-8.
12. Moss SE, Klein R, Klein BEK, Spennetta TL, Shrago ES. Methodologic considerations in measuring glycosylated hemoglobin in
epidemiologic studies. J Clin Epidemiol. 1988;41:645-649.
FULL TEXT
|
ISI
| PUBMED
13. Klein R, Klein BEK, Moss SE. Visual impairment in diabetes. Ophthalmology. 1984;91:1-9.
ISI
| PUBMED
14. Klein R, Klein BEK, Magli YL, et al. An alternative method of grading diabetic retinopathy. Ophthalmology. 1986;93:1183-1187.
ISI
| PUBMED
15. Grading diabetic retinopathy from stereoscopic color fundus photographs—an
extension of the modified Airlie House classification: ETDRS report No. 10. Ophthalmology. 1991;98:786-806.
ISI
| PUBMED
16. Early Treatment Diabetic Retinopathy Study Research Group. Risk factors for progression of diabetic retinopathy: ETDRS report
No. 12. Ophthalmology. 1991;98:823-833.
ISI
| PUBMED
17. Klein BEK, Davis MD, Segal P, et al. Diabetic retinopathy: assessment of severity and progression. Ophthalmology. 1984;91:10-17.
ISI
| PUBMED
18. ETDRS Research Group. Photocoagulation for diabetic macular edema. Arch Ophthalmol. 1985;103:1796-1806.
FREE FULL TEXT
19. McHorney CA, Ware JE, Raczek AE. The MOS 36-Item Short-Form Health Survey (SF-36), II: psychometric
and clinical tests of validity in measuring physical and mental health constructs. Med Care. 1993;31:247-263.
ISI
| PUBMED
20. Ware JE, Kosiniski M, Keller SD. SF-36 Physical and Mental Health Summary Scales:
A User's Manual. 34th ed. Boston, Mass: New England Medical Center; 1994.
21. SAS Institute. SAS/STAT User's Guide, Version 6. 4th ed. Cary, NC: SAS Institute; 1989:1351-1456.
22. McCullagh P, Nelder JA. Generalized Linear Models. 2nd ed. London, England: Chapman & Hall; 1989:151-153.
23. Mangione CM, Lee PP, Gutierrez PR, Spritzer K, Berry S, Hays RD for the NEI-VFQ Field Test Investigators. Development of the 25-item National Eye Institute Visual Function Questionnaire
(VFQ-25). Arch Ophthalmol. In press.
24. Linder M, Chang TS, Scott IU, et al. Validity of the Visual Function Index (VF-14) in patients with retinal
disease. Arch Ophthalmol. 1999;117:1611-1616.
FREE FULL TEXT
25. Mangione CM, Gutierrez PR, Lowe G, et al. Influence of age-related maculopathy on visual functioning and health-related
quality of life. Am J Ophthalmol. 1999;128:45-53.
FULL TEXT
|
ISI
| PUBMED
26. Gutierrez PR, Wilson MR, Johnson C, et al. Influence of glaucomatous field defects on health-related quality of
life. Arch Ophthalmol. 1997;115:777-784.
FREE FULL TEXT
27. Cole SR, Beck RW, Moke PS, Gal RL, Long DT and the Optic Neuritis Study Group. The National Eye Institute Visual Function Questionnaire: experience
of the ONTT. Invest Ophthalmol Vis Sci. 2000;41:1017-1021.
FREE FULL TEXT
28. Klein R, Klein BEK. Relation of glycemic control to diabetic complications and health outcomes. Diabetes Care. 1998;21(suppl 3):C39-C43.
29. Klein BEK, Klein R, Moss SE. Self-rated health and diabetes of long duration: the Wisconsin Epidemiologic
Study of Diabetic Retinopathy. Diabetes Care. 1998;21:236-240.
ABSTRACT
30. Hanninen J, Takala J, Keinanen-Kiukaanniemi S. Quality of life in NIDDM patients assessed with the SF-20 questionnaire. Diabetes Res Clin Pract. 1998;42:17-27.
FULL TEXT
|
ISI
| PUBMED
31. Brown MM, Brown GC, Sharma S, Shah G. Utility values and diabetic retinopathy. Am J Ophthalmol. 1999;128:324-330.
FULL TEXT
|
ISI
| PUBMED
 CiteULike  Connotea  Del.icio.us  Digg  Reddit  Technorati  Twitter
What's this?
THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES
|
Development of a Chinese version of the National Eye Institute Visual Function Questionnaire (CHI-VFQ-25) as a tool to study patients with eye diseases in Hong Kong
Chan et al.
Br J Ophthalmol 2009;93:1431-1436.
ABSTRACT
| FULL TEXT
Visual acuity impairment and vision-related quality of life: the Barbados Eye Studies
Wu et al.
British Journal of Visual Impairment 2009;27:9-24.
ABSTRACT
The National Eye Institute Visual Function Questionnaire in the Macular Telangiectasia (MacTel) Project
Clemons et al.
IOVS 2008;49:4340-4346.
ABSTRACT
| FULL TEXT
Vision-related quality of life in patients with diabetic macular oedema
Hariprasad et al.
Br J Ophthalmol 2008;92:89-92.
ABSTRACT
| FULL TEXT
The social impact of visual impairment
Williams et al.
Br J Ophthalmol 2007;91:986-986.
FULL TEXT
Vision-Related Quality of Life in People With Central Retinal Vein Occlusion Using the 25-Item National Eye Institute Visual Function Questionnaire
Deramo et al.
Arch Ophthalmol 2003;121:1297-1302.
ABSTRACT
| FULL TEXT
Development and Validation of Disease-Specific Measures for Choroidal Melanoma: COMS-QOLS Report No. 2
The Collaborative Ocular Melanoma Study-Quality of
Arch Ophthalmol 2003;121:1010-1020.
ABSTRACT
| FULL TEXT
National Eye Institute Visual Function Questionnaire in the Age-Related Eye Disease Study (AREDS): AREDS Report No. 10
Clemons et al.
Arch Ophthalmol 2003;121:211-217.
ABSTRACT
| FULL TEXT
The Impact of Visual Impairment and Eye Disease on Vision-Related Quality of Life in a Mexican-American Population: Proyecto VER
Broman et al.
IOVS 2002;43:3393-3398.
ABSTRACT
| FULL TEXT
Relation between perceived driving disability and scores of vision screening tests
van Rijn et al.
Br J Ophthalmol 2002;86:1262-1264.
ABSTRACT
| FULL TEXT
|
